Benzeneselenenyl Bromide1

[34837-55-3]  · C6H5BrSe  · Benzeneselenenyl Bromide  · (MW 235.97)

(electrophilic selenium reagent for alkene synthesis2-6)

Physical Data: mp 60-62 °C; bp 134 °C/35 mmHg, 107-108 °C/15 mmHg; sublimes at 25 °C/0.001 mmHg.

Solubility: sol organic solvents such as hexane, CH2Cl2, ether, THF.

Form Supplied in: dark-red crystals; commercially available.

Preparative Method: can be quantitatively prepared in situ by treatment of Diphenyl Diselenide with an equimolar amount of Bromine.2,3,7

Purification: recrystallization from petroleum ether or sublimation.

Handling, Storage, and Precautions: highly toxic, unpleasant smell.

Reaction with Ketones and Enols.

Benzeneselenenyl bromide (PhSeBr) is a useful electrophilic organoselenium reagent which exhibits similar reactivity to Benzeneselenenyl Chloride (PhSeCl). Although the reagent can be substituted by PhSeCl in many reactions, there is a significant difference in reactivity between these reagents.2 Ketones can be efficiently converted into a-phenylseleno ketones through their lithium or copper enolates.3,8 This reaction is useful for the transformation of saturated ketones to a,b-unsaturated ketones and the b-alkylation of a,b-unsaturated ketones (eqs 1 and 2). Similarly, enol acetates are converted into a,b-unsaturated ketones by using benzeneselenenyl trifluoroacetate (PhSeOCOCF3),9 which is prepared in situ by treatment of PhSeCl or PhSeBr with Silver(I) Trifluoroacetate (eq 3).3,4 Silyl enol ethers react with PhSeBr to provide a-phenylseleno ketones and aldehydes in good yields (eq 4).10 On the other hand, PhSeBr adds to enol ethers forming bromoselenenylation adducts regioselectively (eq 5).11 Unlike PhSeCl, PhSeBr does not usually react well with ketones and aldehydes to form a-phenylseleno carbonyl compounds.3

Reaction with Carbanions.

a-Lithiated nitriles12 and nitroalkanes13 rapidly react with PhSeBr to afford the corresponding a-phenylseleno compounds, which are oxidized to a,b-unsaturated nitriles and nitroalkanes, respectively (eqs 6 and 7).

Addition to Alkenes.

PhSeBr reacts with alkenes in aprotic organic solvents to provide bromoselenenylation adducts efficiently.5 This addition is considered to proceed via a seleniranium ion, a selenium-containing 3-membered cyclic cation, and trans adducts are obtained exclusively. For terminal alkenes the regioselectivity of the addition can be controlled by changing the reaction conditions (eq 8).6 The products can be easily transformed to vinylic selenides,6 vinylic and allylic bromides,14a or a-phenylseleno ketones.14b When the reaction is carried out in alcohol or carboxylic acid, oxyselenenylated products of alkenes are obtained in high yields (eq 9).5,15

Alkynyl Selenide Synthesis.

Terminal alkynes undergo electrophilic substitution by treatment with the reagent prepared from PhSeBr and Silver(I) Nitrite, providing alkynyl selenides in good yields (eq 10).16

Reaction with Ketonic Hydrazones.

In the presence of t-Butyltetramethylguanidine, a strong base, ketonic hydrazones smoothly react with PhSeBr to give phenyl vinyl selenides (eq 11).17 This reaction requires an excess amount of PhSeBr.

Related Reagents.

A number of chiral electrophilic selenium reagents have been tested for their possible use in asymmetric synthesis (addition to alkenes, eq 9). Diastereomeric excesses as high as 79% have been achieved for (1) (R = N-(2,4-dinitrophenyl)prolinoyl),18 and 93% for the triflate derived from (2).19 Little asymmetric induction was seen in the addition of (3) to alkenes.20 See also Benzeneselenenyl Chloride, Benzenesulfenyl Chloride, Phenyl Selenocyanate, 2-Pyridineselenenyl Bromide.

1. (a) Clive, D. L. J. T 1978, 34, 1049. (b) Reich, H. J. ACR 1979, 12, 22. (c) Nicolaou, K. C.; Petasis, N. A. Selenium in Natural Products Synthesis; CIS: Philadelphia, 1984. (d) The Chemistry of Organic Selenium and Tellurium Compounds; Patai, S.; Rappoport, Z., Eds.; Wiley: New York, 1986; Vol. 1. (e) Paulmier, C. Selenium Reagents and Intermediates in Organic Synthesis; Pergamon: Oxford, 1986. (f) Organoselenium Chemistry; Liotta, D., Ed.; Wiley: New York, 1987.
2. Sharpless, K. B.; Lauer, R. F.; Teranishi, A. Y. JACS 1973, 95, 6137.
3. Reich, H. J.; Renga, J. M.; Reich, I. L. JACS 1975, 97, 5434.
4. Clive, D. L. J. CC 1973, 695.
5. Sharpless, K. B.; Lauer, R. F. JOC 1974, 39, 429.
6. Raucher, S. JOC 1977, 42, 2950.
7. (a) Behaghel, O.; Seibert, H. CB 1932, 65, 812. (b) Pitteloud, R.; Petrzilka, M. HCA 1979, 62, 1319.
8. Reich, H. J.; Renga, J. M.; Reich, I. L. JOC 1974, 39, 2133.
9. Reich, H. J. JOC 1974, 39, 428.
10. Ryu, I.; Murai, S.; Niwa, I.; Sonoda, N. S 1977, 874.
11. Petrzilka, M. HCA 1978, 61, 2286.
12. Brattesani, D. N.; Heathcock, C. H. TL 1974, 2279.
13. Sakakibara, T.; Takai, I.; Ohara, E.; Sudoh, R. CC 1981, 261.
14. (a) Raucher, S. TL 1977, 3909. (b) Raucher, S. TL 1978, 2261.
15. Takahashi, T.; Nagashima, H.; Tsuji, J. TL 1978, 799.
16. Hayama, T.; Tomoda, S.; Takeuchi, Y.; Nomura, Y. CL 1982, 1249.
17. Barton, D. H. R.; Bashiardes, G.; Fourrey, J.-L. TL 1984, 25, 1287.
18. Tomoda, S.; Fujita, K.; Iwaoka, M. CC 1990, 129.
19. Deziél, R.; Goulet, S.; Grenier, L.; Bordleau, J.; Bernier, J. JOC 1993, 58, 3619.
20. Reich, H. J.; Yelm, K. E. JOC 1991, 56, 5672.

M. Iwaoka & S. Tomoda

The University of Tokyo, Japan

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